It can be useful for various medical diagnostic purposes to utilize a reflectance spectroscope to analyze samples of body fluid, for example, to determine the presence of a particular substance in a person's urine. As is known, reflectance spectroscopy uses the linear relationship between absorbance and concentration of an absorbing species (Beer's law), to determine the contents of a sample. An unknown concentration of an analyte can be determined by measuring the amount of light that a sample absorbs and applying Beer's law. If the absorptivity coefficient of the analyte is not known, the unknown concentration can be determined using a working curve of absorbance versus concentration derived from standards.
Reflectance spectroscopy is the study of light as a function of wavelength that has been reflected or scattered from a solid, liquid, or gas. A conventional reflectance spectroscope, often referred to as a “reflectometer,” may be used to determine optical characteristics, e.g., the color seen by an observer, of a sample, such as a urine sample disposed on a white non-reactive reagent pad. By illuminating such a sample and detecting/recording the intensity of the reflected light at specific wavelengths, the sample's optical signature can be correlated to known optical signatures, and thus the sample can be identified as containing one or more particular substances.
For example, laboratory-based reflectance instruments are used to measure important properties and relative levels of key analytes in urine by measuring relative reflectance, usually from various specific pads, on a urine dipstick. Examples of important properties include pH, the presence of blood, and specific gravity. Examples of key urine analytes include, but are not limited to, glucose, urobilinogen, nitrite, and protein. Optical instruments with sufficient resolution can be used to read the relatively thin (about 1 mm in width) colored lines that develop on reagent pads or strips from lateral flow (or chromatographic) immunoassays. Such colored lines are usually due to the specific immunochemical binding of colored particles such as colloidal gold or dye-infused polystyrene microparticles. Examples of lateral flow immunoassays that can be read on an instrument include the qualitative assessment of urinary or serum levels of hGC (pregnancy), the presence of Streptococcus A from throat swabs, and the detection of various drugs of abuse (e.g., cocaine, morphine, barbiturates, amphetamines) observed in urine.
Many optical inspection machines are small enough and inexpensive enough to be usable in physician offices and smaller laboratories, for example, and therefore are able to provide individual doctors, nurses and other caregivers with powerful medical diagnostic tools.
For example, U.S. Pat. No. 5,654,803, which is assigned to the assignee of the present disclosure, discloses an optical inspection machine for determining non-hemolyzed levels of occult blood in urine using reflectance spectroscopy. The machine is provided with a light source for successively illuminating a plurality of different portions of a reagent pad on which a urine sample is disposed, and a detector array for detecting light received from the reagent pad and generating a plurality of reflectance signals in response to light received from a corresponding one of the different portions of the reagent pad. The machine is also provided with means for determining whether the magnitude of one of the reflectance signals is substantially different than the magnitude of another of the reflectance signals. Where the body-fluid sample is urine, this capability allows the machine to detect the presence of non-hemolyzed levels of occult blood in the urine sample.
U.S. Pat. No. 5,877,863, which is also assigned to the assignee of the present disclosure, teaches an optical inspection machine for inspecting a liquid sample, such as urine, using reflectance spectroscopy. The machine includes a readhead for illuminating a target area substantially uniformly via only a single light-emitting diode and receiving light from the target area so that reagent tests may be performed. The readhead is provided with a housing, first and second light sources mounted in a fixed position relative to the housing, a light guide mounted to receive light from each of the light sources which conveys, when only one of the light sources is illuminated, substantially all of the light from the light source to illuminate a target area substantially uniformly, and a light detector coupled to receive light from the target area. Each of the first and second light sources is composed of only a single light-emitting diode for emitting substantially monochromatic light of a different wavelength.
The optical inspection machines can provide individual doctors, nurses and other caregivers with powerful medical diagnostic tools. These optical inspection machines, however, are not small enough to make shipping the machines (e.g., via the U.S. postal service, or express mail services) between a physician's office or laboratory and the manufacturer convenient and inexpensive. Having a tool and method for verifying the performance of, or troubleshooting, an optical inspection machine in-situ, e.g., at a physician's office or laboratory, could prevent unnecessary shipment of machines for repair when incorrect readings are produced not by a malfunctioning or defective machine but by non-machine problems such as operator error or damaged or defective reagent strips.
Co-pending International Patent Application Serial No. PCT/US2004/017344 (Publication No. WO 2005/001444), which is assigned to the assignee of the present disclosure and which is incorporated herein by reference, discloses an apparatus for verifying proper operation of an optical inspection machine. The apparatus includes a row of colored segments that simulate reagent pads containing known types of analytes at known concentrations positioned so that the row of colored segments can be illuminated by the readhead of the optical inspection machine. If the optical inspection machine provides results that correspond to the known types and concentrations of analytes, then the machine is operating properly. According to one embodiment, the rows of colored segments are colored ink provided on a paper insert.
What is still desired are new and improved apparatus and methods for verifying proper operation of an optical inspection machine, such as those used in medical diagnostics. Preferably, the new and improved apparatus and methods will provide the ability to verify the operation of optical inspection machines using a compact, portable, easy-to-use and inexpensive device. The new and improved apparatus will also be thermally and optically stable and relatively easy to re-produce on a consistent basis.